(1) Field of the Invention
The present invention relates to a positioner seek control system of a disk apparatus, and more particularly to a positioner seek control system of an optical disk apparatus for moving a light beam to a target track in a positioner seek mode in which an optical head is moved by a velocity control of a positioner which drives the optical head.
Generally, in a seek operation in an optical disk apparatus, the beam is moved from its actual position to a target track position. There are two kinds of seek operations, i.e., a lens seek operation and a positioner seek operation. When the distance between the actual position of an object lens and a target track position is as small as, for example, 0.1 mm or smaller, the lens seek operation is carried out by directly moving an object lens by means of a tracking actuator, wherein a positioner is activated to keep the object lens in its neutral position. When the distance is larger than 0.1 mm, for example, the positioner seek operation is carried out. In the positioner seek operation, the tracking actuator carrying the object lens is conventionally locked in its neutral position, and the positioner is activated to move the object lens close to the target track position. Once the object lens comes sufficiently close to the target track position, the lock is released and a fine control is carried out to follow an eccentricity of the rotating medium. The present invention relates to an improvement of the positioner seek control.
(2) Description of the Related Art
In a conventional positioner seek control of an optical disk apparatus, the number of tracks crossed by the beam during the seek operation is counted by using a tracking error signal (TES) so that the beam is made to accurately seek the target track position. This positioner seek operation is referred to as a direct track counting method. During this positioner seek operation, conventionally, the velocity of the positioner (VCM) is controlled in a state in which both a track servo circuit, which makes the beam follow the tracks, and a position servo circuit, which removes the influence of an eccentricity of a rotating medium or of an offset from a neutral position of the tracking actuator, are disabled, i.e., are turned off, and simultaneously a tracking actuator lock (or "trocking actuator lock servo") circuit for maintaining the tracking actuator at the neutral position is enabled, i.e., is turned on.
However, when the tracking actuator lock servo circuit is turned on simultaneously with the turning off of the track servo circuit and the position servo circuit, the tracking actuator starts to return to its neutral position if the tracking actuator is not already positioned at the neutral position. Since the positioner is not sufficiently accelerated at the beginning of the positioner seek operation, the beam may move in the reverse direction opposite to the target track due to the returning of the tracking actuator. As a result, a miscount of tracks may be effected, and therefore, to avoid the miscounting, the positioner seek operation cannot be finished by a single seek operation, but two or more seek operations may be necessary.
Accordingly, it has been desired to provide a positioner seek control system which does not produce a miscount of tracks at the start of a positioner seek operation.